Planar array antennas, when imposed to cover multiple directions, suffer from scan loss. Since the projected aperture decreases as the beam is steered away from the broadside position which is normal to the ground surface and centered to the surface itself, it follows then that broadside excitation of a planar array yields maximum aperture projection. Accordingly, when such an antenna is made to come off the normal axis, the projected aperture area decreases causing a scan loss which is a function of cosine having a value 1 with the argument of zero radians (normal) and having a value 0 when the argument is ##EQU1##
There are a number of methods of beam steering using matrix type beam forming networks that can be made to adjust parameters as directed from a computer algorithm. This is the basis for adaptive arrays. When a linear planar array is excited uniformly (uniform aperture distribution) to produce a broadsided beam projection, the composite aperture distribution resembles a rectangular shape. When this shape is Fourier transformed in space, the resultant pattern is laden with high level side lobes relative to the main lobe. The ##EQU2## function is thus produced in the far-field pattern. In most practical applications these high level side lobes are an undesirable side effect.
Furthermore, an array excited in this manner results in a radiation pattern having a front to back ratio insufficient to avoid co-channel interference with devices operating behind the array. As such reuse of a particular frequency radiating from the array is unnecessarily limited.
Accordingly, a need exists in the art for an antenna system which provides for beam steering without using adaptive techniques.
A further need exists in the art for such an antenna system whereby the beam aperture is relatively constant and broadside to its intended direction without producing undesirable high level side lobes.
A still further need exists in the art for an antenna system having a front to back ratio such that a frequency may be reused directly behind the antenna system without significant co-channel interference.
A yet further need exists in the art for an antenna system providing elevational "down-tilt" providing illumination of a predetermined area in order to allow frequency reuse by additional such antenna systems.
These and other objects and desires are achieved by an antenna design which relies on the simple geometry of conical shapes to provide a more natural beam steering.